1. Field of the Invention
This invention relates to an electrostrictive effect element for converting electric energy into mechanical energy using an electrostrictive effect of a solid, and a method of producing the same.
2. Description of the Prior Art
Electrostrictive effect elements have electrodes which are made of a metal film or the like and formed respectively on the opposing surfaces of an electrostrictive solid material and use an electrostrictive strain generated in the solid material when a voltage is applied across the electrodes thus formed. In this case, the electrostrictive strain generated in the electric field direction (longitudinal electrostrictive strain) is generally larger than the electrostrictive strain generated in the direction perpendicular to the electric field direction (transverse electrostrictive strain), so that the use of the former is higher in the energy conversion efficiency than that of the latter.
With the electrostrictive effect element using the transverse electrostrictive strain, when the size of the element in the direction perpendicular to the electric field direction is increased with an applied voltage kept constant, a displacement amount proportional thereto can be obtained. On the other hand with the electrostrictive effect element using the longitudinal electrostrictive strain, even when the size of the element in the electric field direction is increased with an applied voltage kept constant, the displacement amount cannot be increased because intensity of the electric field inside the element is decreased. The amount of strain to be generated, or the displacement amount, is proportional to the intensity of the electric field inside the element. As a result, in order to obtain a larger amount of displacement with an electrostrictive effect element utilizing the longitudinal electrostrictive effect, it is required to increase the intensity of the electric field inside the element. In this case, however, in order to increase the voltage to be applied, it is necessary to use a power source which is large and expensive, which is pointed out as a problem to be overcome with respect to the dangers of handling it.
Accordingly, previously, an electrostrictive effect element of an integrally laminated ceramic capacitor structure as shown in FIGS. 1 and 2 has been proposed. The electrostrictive effect element as discussed above comprises a laminated body 1 having a plurality of electrostrictive material layers laminated to form a columnar body having a rectangular cross-section, a plurality of plate-like internal electrodes 2a and a plurality of plate-like internal electrodes 2b respectively disposed in a evenly spaced manner in the longitudinal direction inside the laminated body 1, and external electrodes 3a and 3b provided respectively on the opposing side surfaces of the columnar laminated body 1. The internal electrodes 2a and 2b respectively are alternately disposed in the longitudinal direction of the laminated body 1. The internal electrodes 2a are electrically connected to the external electrode 3a, and the internal electrodes 2b are electrically connected to the external electrode 3b. As made clear from FIG. 2, the internal electrodes 2a and 2b are connected only to the corresponding one of the external electrodes 3a and 3b, and a superposed area 4 (rectangular area at the center of FIG. 2) of the internal electrodes 2a and 2b becomes small as compared with the cross-sectional area of this electrostrictive effect element. The space between the adjacent internal electrodes 2a and that between the adjacent internal electrodes 2b respectively can be made in an order of magnitude several tens microns (.mu.m) by the conventional chip-type capacitor technology, so that the distance between the internal electrodes 2a and 2b adjacent to each other can be made small by introducing such a structure as shown in FIGS. 1 and 2. As a result, such an electrostrictive effect element can be practically realized that uses the longitudinal effect and can be driven by applying a low voltage.
However, there may arise the following problems on the conventional electrostrictive effect element shown in FIGS. 1 and 2:
When a voltage is applied across the external electrodes 3a and 3b, the superposed area 4 of the internal electrodes 2a and 2b is deformed in accordance with an intensity of the electric field due to strain generated in an electrostrictive material, and non-superposed areas 5a and 5b of the internal electrodes 2a and 2b and an area 6 not existing the internal electrodes 2a and 2b are not deformed, so that a stress concentration will form at their boundaries. Particularly, in case of an element having the internal electrodes 2a and 2b in a multi-layered structure, when a high voltage is applied for obtaining a larger displacement amount, the stress created will become large, making the element itself easily mechanically damaged.
Thus, an object of the present invention is to provide an electrostrictive effect element which is not mechanically damaged even when a high voltage is applied or when the internal electrodes thereof are formed in multiple layers, and its production method.